The invention generally relates to methods for synthesizing aminosulfur trifluorides and more particularly to methods for synthesizing dialkyl, diaryl, and arylalkyl aminosulfur trifluorides.
In view of the importance of organo-fluorine compounds in the pharmaceutical and agrochemical industries, efforts aimed at the development of simple, safe, and efficient methods for their synthesis have escalated in recent years. The conversion of carbon-oxygen to carbon-fluorine bonds by nucleophilic fluorinating sources (deoxofluorination) represents one such technique which has been widely used for the selective introduction of fluorine into organic molecules. This transformation has been accomplished routinely with dialkylaminosulfur trifluorides, such as DAST (NEt.sub.2 SF.sub.3) and more recently with bis(2-methoxyethyl) aminosulfur trifluoride.
Middleton, 40(5) J. Org. Chem. 574 (1975), describes a process for obtaining dialkylaminosulfur trifluorides, such as DAST, in a two-step process starting from a secondary amine. The amine is silylated with trimethyl silyl chloride or hexamethyl disilazane. After isolation, the silylated amine is reacted with sulfur tetrafluoride to obtain the trifluoride.
As a two-step process, the Middleton process is typically carried out in two reaction vessels. In addition, the process requires the isolation of a pure intermediate, adding to the complexity and cost of the process.
SU Patent No. 1864289 (Markovskii et. al.) describes a more concise process for preparing dialkylaminosulfur trifluorides, as well as an arylalkyl aminosulfur trifluoride. Markovskii et al. prepared aminosulfur trifluorides in a one-step reaction by reacting the corresponding secondary amine with sulfur tetrafluoride in the presence of an amine base that produces a solid amine-HF adduct. This adduct is filtered to obtain the trifluoride in solution of the reaction solvent. Unfortunately, it is difficult to cleanly remove the solid amine-HF adduct from the product because small particles of adduct can escape the filter. In addition, a small amount of adduct is soluble in the reaction solvent and is retained in the product after filtration and evaporation of the solvent.
Accordingly, it is desired to provide a method for producing aminosulfur trifluorides which does not suffer from the aforementioned deficiencies of prior art methods.
All references cited herein are incorporated herein by reference in their entireties.